Method and apparatus for internetworking ethernet and mpls networks

ABSTRACT

MPLS networks offering PW or VPLS services may be interconnected with Ethernet networks implemented according to 802.1ah or 802.1Qay. The MPLS network may be a core and offer services to the Ethernet access networks, or vise-versa. Additionally, a mixture of different types of access networks may be interconnected by an MPLS core or an Ethernet core. Both network interworking and service interworking are provided. OAM fault detection may be implemented via maintenance entities extending across the network or end to end depending on the combination of networks and services offered by the networks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/016,190, filed Jan. 17, 2008, entitled METHOD AND APPARATUS FORINTERNETWORKING ETHERNET AND MPLS NETWORKS, which claims the benefit ofand priority from U.S. Provisional Patent Application No. 60/880,816,filed Jan. 17, 2007 entitled PBB/PBT MPLS INTERWORKING, the contents ofwhich both are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication networks and, moreparticularly, to a method and apparatus for interworking Ethernet andMPLS networks.

2. Description of the Related Art

The various network elements on the communication network communicatewith each other using predefined sets of rules, referred to herein asprotocols. Different protocols are used to govern different aspects ofthe communication, such as how signals should be formed for transmissionbetween network elements, various aspects of what the protocol dataunits should look like, how packets should be handled or routed throughthe network by the network elements, and how information associated withrouting information should be exchanged between the network elements.

Ethernet is a well known networking protocol that has been defined bythe Institute of Electrical and Electronics Engineers (IEEE) as standard802.1. Conventionally, Ethernet has been used to implement networks inenterprises such as businesses and campuses, and other technologies havebeen used to transport network traffic over longer distances. As theEthernet standards have evolved over time, Ethernet has become moreviable as a long distance transport technology as well.

The original Ethernet standard allowed a source address (SA) andDestination Address (DA) to be specified. Over time, several additionalfields have been added to allow other values to be designated withrespect to a particular Ethernet frame. The original Ethernet frameformat specified by IEEE 802.1 includes a source address (C-SA) and adestination address (C-DA). IEEE 802.1Q added a Customer VLAN tag(C-Tag) which includes an Ethertype, TCI information, and customer VLANID. IEEE 802.1ad added a provider VLAN tag (S-Tag), which also includesan Ethertype, TCI information, and subscriber VLAN ID. The C-Tag allowsthe customer to specify a VLAN, while the S-Tag allows the serviceprovider to specify a VLAN on the service provider's network for theframe. These tags also allow the customer and subscriber to specifyother aspects which are not relevant to an understanding of thecontribution disclosed herein. When a network is implemented using802.1ad it may be referred to as Q in Q encapsulation or ProviderBridging (PB). A domain implemented using this Ethernet standard will bereferred to as a Provider Bridging (PB) domain.

The Ethernet standard has evolved to also allow for a secondencapsulation process to take place as specified in IEEE 802.1ah.Specifically, an ingress network element to a service provider's networkmay encapsulate the original Ethernet frame with an outer MAC headerincluding a destination address on the service provider's network(B-DA), a source address on the service provider's network (B-SA), aVLAN ID (B-VID) and a service instance tag (I-SID). The combination ofcustomer MAC addresses C-SA and C-DA with the I-SID are commonlyreferred to as the I-Tag. A domain implemented using this Ethernetstandard will be referred to as a Provider Backbone Bridging (PBB)domain.

There are also two other Ethernet standards that have been developed orwhich are in the process of being developed that may be used in one ormore of the domains. Specifically, IEEE 802.1Qay specifies a way for thenetwork elements to switch traffic based on the B-DA and B-VID ratherthan just forwarding the traffic according to the B-DA. The header ofthe frames forwarded on an Ethernet network established using thistechnology is not changed, but the manner in which the information isused is changed to allow forwarding to take place in a different manner.A network domain that forward traffic using this forwarding paradigmwill be referred to as Provider Backbone Trunking (PBT). In IEEE802.1Qay, PBT is commonly referred to as Provider BackboneBridges—Traffic Engineering (PBB-TE). Thus, the term PBT will be usedherein to refer to a network implemented according to this standard.

PBB, PB, and the original Ethernet standard use a spanning tree protocolto determine which links should be used to broadcast traffic on thenetwork and which links should be used to forward unicast traffic on thenetwork. To overcome some of the shortcomings of using spanning trees,another Ethernet control plane is in the process of being developed asIEEE 802.1aq, in which a shortest path routing protocol such asIntermediate System to Intermediate System (IS-IS) or Open Shortest PathFirst (OSPF) is used in the control plane to establish forwarding pathsthrough the network. Traffic on the domain may then be forwarded basedon the B-DA and B-VID in a manner similar to PBT, but from a controlperspective a shortest path routing protocol is used instead of aspanning tree to define routes through the network. A domain implementedin this manner will be referred to herein as a Provider Link StateBridging (PLSB) domain. PLSB is described in greater detail in U.S.patent Ser. No. 11/537,775, filed Oct. 2, 2006, entitled “Provider LinkState Bridging,” the content of which is hereby incorporated herein byreference. Since PLSB refers to the control plane, it may be used tocontrol forwarding of packets while allowing encapsulation of thepackets using PB, PBB, or PBT as described above.

MPLS is another commonly used networking protocol. MPLS specifies a wayin which a label switched path may be established through a network.When a packet is received at an MPLS Label Edge Router (LER) the LERwill determine the destination LER for the packet, attach a label to thepacket, and forward the packet to a first Label Switch Router (LSR) onthe path to the destination LER. The LSR will strip the label from thepacket, look up the label to determine the next label to be applied tothe packet and the next hop for the path, and forward the packet onwardto the next hop. This proceeds hop by hop across the network to causethe packet to be forwarded across the Label Switched Path (LSP) throughthe MPLS network.

The LSP connects a pair of nodes on the MPLS Network. Since more thanone customer may need to transmit traffic between the pair of endpoints,it is desirable to allow multiple customers to share one LSP rather thancreating a new LSP for each customer. In MPLS, this is accomplishedthrough the use of Pseudowires. Pseudowires allow traffic for differentVLANs to be tagged with a service label, so that traffic from multiplecustomers, VPNs, etc., can use a common LSP and be differentiated by theegress LER. A service that utilizes a pseudowire will be referred to asa Virtual Private Wire Service (VPWS).

In addition to pseudowires, a branching mechanism was developed for MPLSthat will allow a given packet that is received at a label switch router(LSR) to be duplicated and passed out of more than one forwarder. Aservice that utilizes this feature of an MPLS network will be referredto as a Virtual Private LAN Service (VPLS). VPLS uses pseudowires to setup the paths through the network but allows the paths defined by thepseudowires to branch to emulate a Local Area Network (LAN).

VPLS uses the signaling protocol described indraft-ietf-12vpn-signaling-08.txt and IETF RFC 4447 to set uppseudowires. The content of each of these protocols is herebyincorporated herein by reference. RFC 4447 introduces the concept of anAttachment Group Identifier (AGI) that may be conceptualized as a VPNidentifier or VLAN identifier. The AGI specifies a logical group offorwarders at the egress node, rather than a particular individualforwarder. When implemented in this manner, an attachment circuitassociated with a particular VPLS or pseudowire is constructed toinclude the Attachment Group Identifier (AGI) that identifies the groupof forwarders, and an Attachment Individual Identifier (AII) thatidentifies a particular forwarder within the group.

In operation, the MPLS network will establish label switched pathsthrough the network using a Label Distribution Protocol (LDP). As partof this process, the LDP will allow the Label Edge Routers (LERs) toexchange AGI/AII pairs that will allow the network to setup thedataplane for the pseudowires. This will set up the forwarders at thenodes to cause the packets to be forward in a specified manner. When aframe arrives at the ingress LER, the ingress LER will check thesignaled value of AGI/AII pairs with local information and apply aservice label as well as a tunnel label. The tunnel label will be usedto forward the frame along the LSP through the MPLS network, while theservice label will be used by the egress node to obtain the context ofthe pseudowire at the egress so that the frame may be sent to thecorrect set of forwarders. The forwarders will then be used to forwardthe traffic to the correct customer/VPN as the traffic exits the MPLSnetwork. The AGI/AII pairs are thus used in the signaling phase ofestablishing the VPLS service by the ingress/egress LERs to coordinatehow frames should be handled at the egress to cause the frames to beforwarded to the correct customers.

To monitor how a network is operating, such as to perform faultdetection, fault isolation, fault confirmation, and other types of faultdetection and remediation, an operator may want to send Operation,Administration, and Maintenance (OAM) service frames across the network.Different OAM flows may be used to monitor different aspects or segmentsof a connection on the network. For example, an OAM flow may be usedend-to-end across the network, may be used to monitor the connectionwithin a particular domain, or may be used to monitor other aspects ofthe connection on the network. A particular OAM flow will be referred toherein as a Management Entity (ME). By monitoring a particular ME thenetwork manager may determine whether connectivity exists across thatportion of the network, and if connectivity does not exist, may enablethe network manager to isolate the fault on the network. When Ethernetnetworks and MPLS networks are required to connect together, a networkmanager may need to be able to define Maintenance Entities across acombined MPLS/Ethernet network

As discussed above, both Ethernet networks and MPLS networks haveimplemented features that will allow traffic from different VLANs to beidentified, and which will also allow traffic associated with particularservice instances within a VLAN to be identified. When the networks areinterconnected, it would be advantageous to allow interworking to occur,either at the network level or service level, so that particularservices may be offered end-to-end across the interconnected network.Additionally, from a management perspective, it would be advantageous toenable OAM Maintenance Entities to be defined to monitor aspects of theMPLS/Ethernet network.

SUMMARY OF THE INVENTION

MPLS networks offering PW or VPLS services may be interconnected withEthernet networks implemented according to 802.1ah or 802.1Qay. The MPLSnetwork may be a core and offer services to the Ethernet accessnetworks, or vise-versa. Additionally, a mixture of different types ofaccess networks may be interconnected by an MPLS core or an Ethernetcore. Where service frames are to be mapped from an ingress Ethernetnetwork to an egress Ethernet network across an MPLS network, the VLANID value will be set to correspond to a PW through the MPLS core toreach the particular egress Ethernet network. Where the MPLS coreimplements VPLS, the destination address may be selected to allow theEthernet network to select the correct VPLS instance. Where an Ethernetcore is used, the Ethernet core may select a tunnel based on thepseudowire label associated with the service frame or based on theB-VID, I-SID, or B-VID and B-DA associated with the service frame.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are pointed out with particularity inthe appended claims. The present invention is illustrated by way ofexample in the following drawings in which like references indicatesimilar elements. The following drawings disclose various embodiments ofthe present invention for purposes of illustration only and are notintended to limit the scope of the invention. For purposes of clarity,not every component may be labeled in every figure. In the figures:

FIGS. 1-3 are functional block diagrams of communication networksshowing three example ways in which Ethernet and MPLS network domainsmay be connected;

FIG. 4 is a functional block diagrams of a reference view of a networkincluding MPLS networks and an Ethernet (PBT) core network;

FIG. 5 is a functional block diagram of a path through the referencenetwork of FIG. 4 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 6 is a functional block diagrams of a reference view of a networkincluding MPLS networks and an Ethernet (PBB) core network;

FIG. 7 is a functional block diagram of a path through the referencenetwork of FIG. 6 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 8 is a functional block diagrams of a reference view of a networkincluding MPLS networks and an Ethernet (PBT/PBB) core network;

FIG. 9 is a functional block diagrams of a reference view of a networkincluding Ethernet (PBT) networks and an MPLS (PW) core network;

FIG. 10 is a functional block diagram of a path through the referencenetwork of FIG. 9 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 11 is a functional block diagram of path through the referencenetwork of FIG. 9 illustrating another format of the headers applied tothe data as it traverses the network according to an embodiment of theinvention;

FIG. 12 is a functional block diagram showing example maintenanceentities that may be implemented in the network of FIG. 9 according toan embodiment of the invention;

FIG. 13 is a functional block diagrams of a reference view of a networkincluding Ethernet (PBT) networks belonging to different domains and anMPLS (PW) core network;

FIG. 14 is a functional block diagram of a path through the referencenetwork of FIG. 13 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 15 is a functional block diagram showing PBT trunk segments in thenetwork of FIG. 13 according to an embodiment of the invention;

FIG. 16 is a functional block diagram showing example maintenanceentities that may be implemented in the network of FIG. 15 according toan embodiment of the invention;

FIGS. 17-19 are functional block diagrams showing several differentinterconnects that may be used to interconnect the PBT and MPLSnetworks;

FIG. 20 is a functional block diagrams of a reference view of a networkincluding Ethernet (PBB) networks belonging to different domains and anMPLS (PW) core network;

FIG. 21 is a functional block diagram of a path through the referencenetwork of FIG. 20 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 22 is a functional block diagrams of a reference view of a networkincluding Ethernet (PBB/PBT) networks and MPLS networks interconnectedover an MPLS (VPLS) core network;

FIG. 23 is a functional block diagram of a path through the referencenetwork of FIG. 22 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention;

FIG. 24 is a functional block diagrams of a reference view of a networkincluding Ethernet (PBB/PBT) networks and MPLS networks interconnectedover an MPLS (PW) core network;

FIG. 25 is a functional block diagram of a path through the referencenetwork of FIG. 24 illustrating the format of the headers applied to thedata as it traverses the network according to an embodiment of theinvention; and

FIG. 25A is a functional block diagram of a path through the referencenetwork of FIG. 24 illustrating another format of the headers applied tothe data as it traverses the network according to an embodiment of theinvention.

DETAILED DESCRIPTION

The following detailed description sets forth numerous specific detailsto provide a thorough understanding of the invention. However, thoseskilled in the art will appreciate that the invention may be practicedwithout these specific details. In other instances, well-known methods,procedures, components, protocols, algorithms, and circuits have notbeen described in detail so as not to obscure the invention.

When an Ethernet network and an MPLS network are interconnected, the twonetworks will pass protocol data units between each other. Depending onhow the networks are connected, service instances on one network may betranslated to service instances on the other network. A system thatinterconnects networks of different types in this manner will bereferred to herein as “service interworking.” Service interworkingimplies that a handoff to another domain is such that the other domainidentifies its service instance (e.g. PW/VPLS) from service frames,translates service frames to its service instance, and transports them.Transformation of service frames is expected inside the other domain inthis case. In an Ethernet/MPLS context, service interworking may occurin various ways. For example, service interworking may occur where theMPLS network identifies its service instance such as PW or VPLS from theI-SID or other service identifier in use on the Ethernet network.

Another way of interconnecting two domains is for the two domains toencapsulate service frames for transport without transforming theservice frames. An interconnection of this nature will be referred toherein as network interworking. In an Ethernet to MPLS context, NetworkInterworking may occur in various ways. For example, networkinterworking may occur where the MPLS network identifies its serviceinstance such as PW or VPLS from the VLAN ID in use on the Ethernetnetwork.

There are many interworking cases that are possible, due to the myriaddifferent types of Ethernet and the several different ways in which anMPLS network may be instantiated. Several ways of interworking MPLS andEthernet networks are set forth below. Since there is a large deployedbase of MPLS networking gear, an emphasis on selecting ways to interworkMPLS and Ethernet networks has been provided that will minimize theamount of modification required on the MPLS networking gear.

FIGS. 1-3 illustrate three example communication networks and show threeexample ways in which Ethernet and MPLS network domains may beconnected. In FIG. 1, Customer Edge (CE) devices 10 connect via anEthernet Access Switch 12 to an aggregation network 14 such as ametropolitan (Metro) area network. The use of an Ethernet Access Switchis optional, and the invention is not limited by the manner in which theCustomer Edge devices 10 connect to the aggregation network.Additionally, Ethernet Access Switches have many common names, such asNetwork Interface Demarcation (NID) and thus many different ways may beused to access the networks described herein. Additionally, throughoutthis description the term “metro” network will be used to refer to anaggregation network. The invention is not limited to an implementationthat interworks a metropolitan area network with a core network,however, as embodiments of the invention may be utilized to interworkEthernet and MPLS domains of any desired size and in any desiredcontext. The metro network is connected to a core network 16, which maybe connected to other metro networks.

The metro networks may be implemented using MPLS and the core networkmay be implemented using Ethernet, as shown in FIG. 1. Alternatively,the core network may be implemented using MPLS and the metro networksmay be implemented using Ethernet as shown in FIG. 2. Stillalternatively, a mixture of Ethernet and MPLS networks may be used toimplement the metro networks and MPLS or Ethernet may be used in thecore as shown in FIG. 3. The Ethernet and MPLS networks thus may beconnected together in many different ways and, accordingly, it may bedesirable to interwork the networks differently depending on theparticular context.

Additionally, two or more of the metro networks may be implemented usinga common control plane, so that the two metro networks are to beconsidered to be one logical network. Interworking another network withthe common metro networks may need to take into account the fact thatthe two metro networks are implemented using a common control plane sothat flows of data may be commonly implemented by the metro networkswithout alteration by the intervening core network. Thus, many differentnetwork scenarios are possible and, depending on the particularimplementation, the manner in which the networks are interworked mayvary as well.

In FIG. 1, the Customer Edge (CE) 10 will pass a packet/frame to theEthernet Access Switch (EAS) 12. The EAS will pass the packet to aMulti-Service Edge (MSE) 18 on the MPLS network which will place thepacket on a Label Switched Path (LSP) across the metro network. The MPLSnetwork may implement pseudo-wires (PW) or Virtual Private LAN Service(VPLS) depending on whether the Label for the packet is selected basedon the packet's IP address or IP address and VLAN ID. The packet will bereceived by another MSE on the edge of the metro network and passed to aSwitching—Provider Edge (S-PE) 20 on the core network.

The metro network 14 in FIG. 1 is an MPLS network having a plurality ofMulti-Service Edge (MSE) network elements configured to receive trafficand put the traffic onto Label Switch Paths (LSP) through the network.The MSE network elements act as Label Edge Routers (LERs) that assignlabels to packets according to the path the packet is to take throughthe MPLS network. The MSE also adds one or more PseudoWire (PW) tags toenable traffic from multiple customers to be multiplexed across a givenLSP through the network. In operation, a MSE will receive a frame fromthe S-PE and assign label and PW tag. The label will be used to forwardthe frame across the MPLS network and the PW tag will be used todemultiplex the frame to identify the customer flow associated with thetag.

The core network in the embodiment of FIG. 1 is an Ethernet networkconfigured to operate using Provider Backbone Bridging (PBB) defined byIEEE 802.1ah (Mac in Mac) or Provider Backbone Transport (PBT) definedby IEEE 802.1Qay. In a PBB network, packets are forwarded across thenetwork based on the destination MAC address in the outer header of thepacket. PBT networks allow traffic engineering to take place on thenetwork to allow explicit paths to be set up across the network based onVLAN ID (VID), and forwarding takes place within the network based onboth the destination address and VLAN ID. Optionally, within the samenetwork a range of VIDs may be used to implement PBT while other VIDscan be used to implement PBB. Thus, the two types of networks maycoexist. In the following description, particular reference may be madeto particular types of Ethernet networks being interworked with MPLSnetworks. This description is not to be construed as an indication thatonly one type of Ethernet network exists, but rather is to be construedas referring to how a particular type of Ethernet technology may beadapted to interwork with an MPLS network. Other Ethernet standards maybe implemented as well, and as new standards are developed the conceptsdisclosed herein may be extended to interoperate with those newstandards where applicable.

In the example shown in FIG. 1, the metro network has a plurality ofMSEs 18 configured to implement user to network interface (UNI)interfaces to enable customers (e.g. CE 10 or EAS 12) to connect to themetro network. On the boundary between the metro network 14 and the corenetwork 16 the network elements will implement Network to NetworkInterfaces (NNIs) to enable the network element to connect to othernetwork elements.

FIG. 2 is similar to FIG. 1, except that the Metro networks areimplemented as Ethernet networks (either PBB, PBT) and the core networkis an MPLS network (PW or VPLS). FIG. 3 is also similar except that themetro networks are a mixture of Ethernet and MPLS, and the core is anMPLS network. Other network scenarios are also likewise possible.

FIG. 4 shows an example network 400 where three MPLS access networks410, 420, 430 (metro networks) are interconnected by a PBT core network450. FIG. 6 shows a similar embodiment in which a PBB core network 650is used to interconnect MPLS metro networks. As mentioned above, as usedherein the term Provider Backbone Trunking (PBT) refers to a networkthat is implemented using Ethernet standard IEEE 802.1Qay, which allowstraffic engineered paths to be established through the network. Themanner in which PBT operates is specified in IEEE 802.1Qay, the contentof which is hereby incorporated herein by reference. The term ProviderBackbone Bridging (PBB) refers to an Ethernet network that isestablished using Mac in Mac encapsulation to allow forwarding withinthe network to occur based on provider MAC addressing rather thancustomer MAC addressing. The manner in which PBB operates is specifiedin IEEE 802.1ah, the content of which is hereby incorporated herein byreference.

In the embodiment shown in FIG. 4, MPLS access networks include NetworkProvider Edge (N-PE) network elements 402 that interface with customers,such as Customer Edge (CE) 404 or User-Provider Edge (U-PE) 406. TheMPLS access networks also include Switching Provider Edge (S-PE) 408that connect to the core network 450. The PBT core network includesProvider Edge (PE) network elements 452 that interconnect the corenetwork with the access networks.

In a scenario such as the one shown in FIG. 4, the MPLS access networksand PBB or PBT core network may be interworked at the network level orthe service level. If the networks are interworked at the network level,the MPLS domain will consider the PBB/PBT domain as a server domain andwill not peer with it. The MPLS domain nodes will peer on either side ofthe PBB/PBT domain, however. The MPLS domain will transmit and receiveEthernet encapsulated frames containing LSP payloads, where Ethernetencapsulation is link local (link here is represented as between twoMPLS peer nodes, which is virtualized over the PBB/PBT domain). ThePBB/PBT domain would therefore receive Ethernet frames which would needto be mapped to PBB/PBT service instances.

Accordingly, from a network interworking standpoint, the PBT domainrequires the MPLS domains to use virtual links (i.e. VLANs) such that anMPLS node only uses a virtual link such that it is dedicated for asingle peer MPLS domain only. By causing a particular MPLS domains touse a different VLAN value or set of VLAN values for each of the otherMPLS domains, the ingress nodes on the PBT core may map the VLAN valuesto PBT trunks in the PBT core to cause the frames to be forwarded to thecorrect MPLS domain. Thus, for example, assume that VLAN 1 was used byMPLS domain X for traffic intended for MPLS domain Y, and that VLAN 2was used by MPLS domain X for traffic intended for MPLS domain Z. Byusing a different VLAN ID for each of the destination MPLS domains, theingress node on the PBT core may select a trunk to carry the traffic toeither MPLS domain Y or MPLS domain Z by looking at the VLAN IDassociated with the frame.

Where different PBT trunks are required to have different trafficengineering requirements, more than one PBT trunk may be implementedbetween the same set of metros. Thus, optionally, a set of VLAN valuesmay be used to designate a set of PBT trunks extending between the pairof metros. If the MPLS domains are not able to implement virtualinterfaces, i.e. implement different VLAN IDs for different destinationMPLS domains, then a PBB core network should be used instead of a PBTcore network. Alternatively, the S-PEs may use different ports (physicalinterface) for each metro such that the PE is able to map traffic todifferent PBT trunks to different metros based on the ingress physicalinterface.

If the networks shown in FIG. 4 are to be interworked at a servicelevel, then the MPLS domains will consider the PBB/PBT domain as a peerdomain. The MPLS domain will transmit and receive Ethernet encapsulatedframes containing a pseudowire payload. Ethernet encapsulation, in thisinstance, will be link local for the link between the MPLS and PBB/PBTnodes. The PBB/PBT domain will receive Ethernet frames, de-encapsulatethe frames to obtain access to the PW encapsulated frames. Thus, wherethe networks are to be interworked at the service level, the PBB/PBTdomain will preferably support Pseudo Wire signaling in line with MS-PW.Alternatively, static configuration may be used as well. Additionaldetails of this type of interworking will be described below inconnection with FIGS. 9-12.

In the Example shown in FIG. 4, the access switch (U-PE) 406 hands offnative service frames to the MPLS access switch (N-PE) 402 to be carriedtransparently over a PseudoWire (PW) service. The N-PE 402 encapsulatesdifferent native services (e.g. TDM) over PWs. The N-PEs establishend-to-end PWs. The S-PEs may optionally run directed LDP sessionsbetween them. The PBT core appears as a single Ethernet link between theS-PEs. The S-PEs also establish LSPs among each other. The PBT coreprovides transport of LSP tunnels. Thus, for example in FIG. 4, S-PE1will establish an LSP with S-PE3 that spans the PBT core. The PBT corewill provide transport service for packets passed along the LSP betweenS-PE1 and S-PE3. Within each MPLS network, an LSP will also be set upbetween the N-PE and S-PE. Thus, for example, an LSP may be set upbetween N-PE 2 and S-PE1 in MPLS network X, and similarly between S-PE3and N-PE 4 in MPLS network Y. The LSP may be one LSP across both MPLSdomains and the PBT domain, or may be individual LSPs in each of thethree segments.

The PEs offer PBT trunks, such that frames entering the PBT networkeither carry tags that are dedicated to connection a MPLS domain withonly a single other domain (i.e. dedicated virtual interfaces asdescribed above) or carry the S-PE's DA with a common tag. The PE willmap frames received from the S-PE to a PBT trunk based on the tagassociated with the frame, or uses the VLAN and DA to identify the PBTtrunk. For resiliency and loop avoidance, the PEs may establish bothprimary and backup trunks.

A packet may be provided with a particular quality of service in theMPLS network. For example, the access switch U-PE or MPLS access switch(N-PE) may set the LSP Exp bits in the MPLS header to indicate aparticular class of service. To allow the Ethernet network to afford thesame quality of service to the packet as it traverses the core network,it may be desirable to map the LSP Exp bits to the B-Tag p-bits in theEthernet header. The p-bits are three bits specified in the B-Tag whichare defined by IEEE 802.1p to be used to indicate a quality of service.Optionally the p-bits associated with the Ethernet header that isapplied to the packet as it traverses the PBT network may be set toprovide a quality of service akin to that associated with the packet inthe MPLS network.

FIG. 5 shows encapsulations that may occur to a packet as it traversesthe network of FIG. 4. In the example shown in FIG. 5, it will beassumed that the packet is received at U-PE2 on MPLS access network Xfrom CE2, and is addressed to CE4 connected to U-PE4 on MPLS accessnetwork Y.

As shown in FIG. 5, the U-PE2 will output a service frame 500 which,when received by N-PE2 will be mapped to a LSP to N-PE4. The LSP to beused to carry the packet from N-PE 2 to N-PE 4 may extend end-to-endbetween the two MPLS networks or may terminate in each MPLS network. Forexample, a first LSP may extend from N-PE2 to S-PE1, a second LSP mayextend from S-PE1 to SPE3, and a third LSP may extend from S-PE3 toN-PE4. Alternatively, a single LSP may extend from N-PE2 to N-PE4. Wheremore than one LSP segment is involved, the end point between the twosegments will separately signal the LSPs and map traffic from one to thenext to complete a path through the network. Similarly, the networkelement in this instance may also map PWs on the different LSP segmentsto allow PW service to extend end-to-end across the network.

In the example shown in FIG. 5, when N-PE2 receives a packet it willassign a LSP label 502 to the packet and a PW label 504 to the packet.The LSP in this instance identifies the path through the network, whilethe PW label allows traffic from multiple customers to be multiplexed onthe same LSP and discerned by the end router so that the differenttraffic may be forwarded to the correct customer on the egress from thenetwork.

In addition to the LSP label and PW label, the N-PE will assign a linklayer Ethernet header (transport header 506) that will be used by thenetwork element to forward the packet toward the next hop on the MPLSnetwork. Each hop on the MPLS network will remove the transport header,read the LSP label, swap the LSP label with a new LSP label, and forwardthe packet toward the next hop on the MPLS network. The manner in whichthe MPLS network operates is not intended to deviate from standardpractice.

When the S-PE receives the packet it will perform a label swap as normaland forward the packet over the LSP that passes through the PBT corenetwork. The PE, upon receipt of the packet, will determine the PBTtrunk to be used to carry the packet as described in greater detailabove. For example, the PE may read the B-DA associated with thetransport header or the B-VID contained in the B-TAG to determine thePBT trunk to be used to carry the packet across the PBT core network.The PE will then encapsulate the packet with a header 508 that will beused to transport the packet across the PBT core network. The header,may be a standard 802.1ah PBB encapsulation header that will be used totransport the packet across the PBT trunk on the PBT core network.

When the packet is received at the egress from the PBT network, the PEwill strip off the header 508 and forward the packet to the S-PE3. TheS-PE 3 will strip off the transport header 506, read the LSP label, andforward the packet toward N-PE4. Where the LSP over the PBT core and theLSP over the MPLS access network Y are different LSPs, the S-PE3 willmap the packet from one LSP to the next before forwarding the packettoward the LPS on MPLS access network Y.

From a resiliency standpoint, the PBT network may implement primary andbackup PBT trunks, so that the PBT trunks may be considered resilient.The MPLS domain can run its own resilient PWs, which are transparent tothe PBT core. The nature of the interconnect determines the level ofvisibility and impact of any failure.

The solution described herein, in connection with FIGS. 4-5, allows thePEs to operate without reference to the PW labels. When dedicatedvirtual interfaces (i.e. VLAN IDs) are used by the S-PEs to forwardtraffic to different MPLS networks, the PEs may operate in a normalmanner by using the VID to identify the I-SID and PBT trunk that are tobe used to create the header 508 for use in transporting the packetacross the PBT network. Additionally, the S-PE is not required to treatthe link through the PBT network as anything other than a regularEthernet link. However, this solution does require an additional 22 byteoverhead for each frame passed across the PBT network, since as shown inFIG. 5 the encapsulation process performed by the ingress PE to the PBTnetwork will result in an 802.1ah MAC header 508 to be applied to theframes as they enter the PBT network. Additionally, if the MPLS networksdo not use virtual interfaces, and hence use the same VID to identifymore than one other MPLS network, the PE may be required to use otherfields to map incoming frames to PBT trunks. For example, the PE may berequired in this instance to determine the I-SID and PBT trunk based onthe DA rather than only the VID.

FIG. 6 shows another example in which a PBB core network implementedusing 802.1ah is used to interconnect MPLS access networks. As shown inFIG. 6, the access switch (U-PE) hands off native service frames to theMPLS access switch (N-PE) to be carried transparently over a PW service.The N-PE encapsulates different native services over pseudowires. TheN-PEs may establish end-to-end PWs or may establish PWs with the S-PEs,and the S-PEs may establish PWs. Thus, the LSP and PWs may extendend-to-end between the N-PEs or may be segmented as described above inconnection with FIGS. 4-5. As with the previous example, the PBB networkwill appear as a single Ethernet link between S-PEs on different MPLSaccess networks, and the PBB core will thus provide transport for theLSP tunnels.

The PEs offer E-LAN service connectivity across the PBB core. E-Line maybe considered a special case of point-to-point E-LAN connectivity acrossthe PBB core. Frames entering the PBB network carry the S-PE's DA andpossibly a tag. PEs offer E-LAN service corresponding to the tag. Oneexample of the tag that may be used in connection with this is the B-VIDcontained in the B-Tag.

When a packet arrives at the PE, the PE will use the B-VID and B-DA(indicating S-PE DA) from the transport header 606 to identify a serviceinstance associated with the packet, and then encapsulate the packet fortransport across a PBB tunnel through the PBB core network. As mentionedabove with respect to the PBT core network, when a PE receives a packetit may be desirable to map the LSP Exp bits to the B-tag p-bits. Thismapping is advantageous as both the EXP bit field and the p-bit fieldare three bits long, so that each accommodates 8 classes of service.

The PBB network may implement either a spanning tree or a link stateprotocol to control the PBB network. For example, it is common for PBBnetworks to implement a spanning tree protocol to implement resiliencyand loop avoidance. Alternatively, a link state protocol such as OSPF orIS-IS may be used to control the network and provide resiliency and loopavoidance.

FIG. 7 shows the encapsulation that may occur as a packet traverses theinterworked MPLS networks and PBB core network. As shown in FIG. 7, theencapsulation process is very similar to the process described above inconnection with FIG. 5. For example, as a service frame enters the MPLSnetwork it will be mapped to an LSP and PW, and encapsulated using a LSPlabel and PW Label. A transport header will be applied to transport thepacket across the MPLS network. The transport headers are mostly linkspecific.

When the packet is received at the S-PE the S-PE will either forward thepacket along the LSP onto the PBB network (where the LSP existsend-to-end between the N-PEs) or will translate the LSP from an LSPsegment on the MPLS access network to an LSP that extends across the PBBcore network. Similarly, the PW label may remain the same on the variousLSP segments or may be translated by the S-PE if the packet is put ontoa new LSP segment at the S-PE. The S-PE will then apply a link header totransport the packet to PE1.

From the S-PE standpoint, regardless of whether the LSP extends fromend-to-end or there are multiple LSP segments, the next hop on the LSPas seen by the S-PE on the first MPLS network is the S-PE on the secondMPLS network. For example, on the path shown in FIG. 7, the next hop forS-PE1 on MPLS access network X is S-PE3 on MPLS access network Y. Thus,the transport header applied by S-PE1 to the packet will point to S-PE3.Upon receipt, the PE will use the data contained in the transport headerto map the packet to a PBB tunnel and apply a PBB header that will beused to forward the packet through the IP network.

From a resiliency standpoint, the PBB tunnels are resilient assumingthat the PBB core is running either xSTP or a link state protocol on thecontrol plane. Similarly, the MPLS domain can run its own resilient PWswhich are transparent to the PBB core. The nature of the interconnectbetween the MPLS networks and the PBB core will determine the level ofvisibility and impact of a failure on the network.

One benefit of using a PBB core to interconnect multiple MPLS domains isthat the PEs on the PBB core are transparent to the PW labels. Statedanother way, the MPLS network is not aware of the PBB core and canimplement PWs that span across the PBB core without requiringmodification to the manner in which the S-PEs operate. Additionally, thePEs on the PBB core are not required to operate differently but rathercan implement normal forwarding behavior and use the VID and DA of thetransport header applied to incoming packets to identify the I-SID andPBB tunnel to be used to transport the packet across the PBB network.

Like the previous example, however, the PE will add a 22 byte header toeach frame of the packet which increases the overhead associated withtransmitting the packet across the PBB network. Depending on the natureof the traffic this may or may not be a concern. Additionally, the PBBnetwork is still required to implement one or more spanning treeinstances or a link state protocol to avoid loop formation and forresiliency.

The previous two examples, shown in FIGS. 4-5 and 6-7, assumed that theMPLS network was implementing PseudoWires (PWs). It is also possible forthe MPLS network to offer Virtual Private LAN Service (VPLS) tocustomers. Where the MPLS network implements VPLS rather than PWs, theaccess switch (U-PE) will hand off native service frames to the MPLSaccess switch (N-PE) to be carried transparently over a VPLS service.

To implement VPLS services, the N-PEs will establish a mesh of PWsinterconnecting all of the N-PEs with all of the S-PEs. The S-PEs willalso support spokes to all other S-PEs on all other metros. FIG. 8 showsan example of this in which a mesh of PWs 802 has been established inthe MPLS access network X, and a mesh of PWs 804 to other S-PEs on otherMPLS access networks.

When the N-PE receives a packet, it will encapsulate the frame with a PWlabel and LSP label and forward the packet across the PW to the S-PE.The S-PE replicates the frame at handoff, if the service instance spansmore than one remote metro, and forwards multiple copies of the frameacross the PWs to each of the S-PEs on each of the remote metros.

The PEs on the PBB/PBT network offer E-LINE/E-LAN service forconnectivity across the PBB/PBT core. Frames entering the PBT/PBB corehave a link level transport header including the DA of the intended S-PEon the remote metro network. The transport header may also include aVLAN ID or other tag. The PE uses the VLAN or the VLAN and MAC (DA) toidentify the service instance in the PBB/PBT network that should be usedto transport the packet across the PBB/PBT network. The PE willencapsulate the packet in a PBB/PBT tunnel (using the PBB encapsulationprocess of 802.1ah, as described above in greater detail) and forwardthe packet across the network. Thus, the interworking between PBB/PBTnetworks and the MPLS network may be implemented, from a PE standpoint,in the same manner regardless of whether the MPLS network is offering aPW service or VPLS service.

Within the MPLS networks, a reservation protocol such as RSVP may be runto implement redundant spokes between each pair of metros. RSVP allowstraffic engineered paths to be established through a network. Hence,RSVP may be used to create two separate paths between each pair ofN-PE/SPE to allow for redundant paths to be created within the MPLSnetworks. The resilient paths within the metro are transparent to thePBB/PBT core.

As a summary, when a PBB or PBT network is implemented as the corenetwork, and MPLS networks are used to implement the metro networks, thePE must recognize Ethernet frames encapsulating the MPLS payload fromthe MPLS networks. The PE may use the VLAN or the VLAN and DA from thetransport header applied by the S-PE to map the packets to appropriatePBB or PBT tunnels through the network. Where the SPEs are able toimplement VLAN sets containing one or more VLAN per remote metro, the PEmay identify the PBB/PBT tunnel from the VLAN and map the packets to theappropriate PBB/PBT tunnel according to the VLAN. Where the SPEs are notable to implement one VLAN per remote metro, the PE may use the DA alongwith the VLAN to map the packets to the appropriate PBB/PBT tunnel.Optionally, the PE may also map the LSP EXP bits to PBB/PBT tunnelp-bits to allow the same quality of service features to be providedend-to-end across the MPLS/PBB/MPLS or MPLS/PBT/MPLS network.

When a PBB/PBT trunk fails, an alarm indication signal (AIS) may betransmitted toward the MPLS domain on a per-VLAN basis. This will allowthe alarm indication signal to be propagated to the MPLS domain on thevirtualized links to enable the MPLS domain to failover traffic to abackup path. By implementing AIS signaling from the PBB/PBT domain tothe MPLS domain, the MPLS domain is not required to run end-to-endmaintenance entities over the PBB/PBT domain, and may thus treat thePBB/PBT tunnels as a link. Implementation of this feature would requirethe S-PEs to be configured to implement Ethernet OAM signaling to allowthe S-PEs to interpreted receipt of an AIS as a failure indicationrather than a generic Ethernet frame. Accordingly, implementation ofthis feature may require modification of the S-PE to enable it to beimplemented on the network.

FIGS. 9 and 10 show an example network in which Ethernet access (Metro)networks 910, 920, 930, are interconnected by an MPLS core network 950.As shown in FIG. 9, Ethernet network includes a Provider Edge (PE) thatreceives traffic from customers and places the traffic onto the Ethernetnetwork. Switching PEs (S-PE) 904 forward the traffic from the Ethernetnetwork to the MPLS core network. The MPLS core network implementsMulti-Service Edge (MSE) network elements 906 which receives trafficfrom the Ethernet network and puts the traffic onto Label Switched Paths(LSPs) through the MPLS core. The MPLS core may implement PseudoWire(PW) or Virtual Private LAN Service (VPLS) service.

From a network interworking perspective, the Ethernet domain wouldconsider the MPLS domain as a server domain and would not peer with it.Ethernet domain nodes would peer on either side of the MPLS domain. TheEthernet domain would transmit and receive Ethernet encapsulated framescontaining native payload. Optionally, the S-PE nodes may transmit PWencapsulated frames.

MSEs on the MPLS domain would receive Ethernet frames which would needto be mapped to PW or VPLS service instances. If the MPLS domainimplements PW service, interworking can be accomplished by requiring theEthernet domains to use correct B-VIDs to identify egress Metro domains,since the MSE is not able to map B-MAC addresses into PWs. Where theMPLS domain implements VPLS service, the MSE similarly determines theVPLS service instance based on the B-VID in the case of networkinterworking.

Where the networks are to be interworked at the service level, theEthernet domain will consider the MPSL domain as a peer domain. TheEthernet domain transmits and receive Ethernet encapsulated frames. TheMPLS domain receives Ethernet frames and de-encapsulates the frames tohave visibility to the native service payload. Accordingly, serviceinterworking requires the Ethernet domain to support PW signaling,unless static configurations are allowed at the edge of the domains.

FIGS. 9-10 show a single PBT implemented across a MPLS PW core. As shownin FIG. 9, the Ethernet access switch (U-PE) hands off Ethernet framesto the metro access switch (PE) to be carried transparently over anE-line service. The U-PE may encapsulate different native services,however the PE does not have visibility to these native services, butrather simply sees Ethernet frames.

The PE offers either a port-based E-line or a tagged E-line service. Aport-based E-line service encapsulates all frames received on aparticular port as a particular service instance. Tagged E-line service,by contrast, encapsulates frames received with a particular VLAN set,including one or more VLAN IDs, into a particular service instance fortransmission over the PBT network. The PE will then encapsulate theframes into a PBT trunk for transmission across the PBT network. TheI-SID is end-to-end unique across the combined Metro domains and, hence,the I-SID may be used end to end to identify the service instanceassociated with the frame.

According to an embodiment of the invention, the B-VIDs assigned toframes are allocated as belonging to a particular metro pair. Thus, inFIG. 9, traffic from PBT metro X with a destination of PBT metro Y wouldbe assigned a first B-VID, traffic from PBT metro X to PBT metro Z wouldbe assigned a second B-VID, etc. Each pair would thus use one particularB-VID. Optionally, traffic in the reverse direction (i.e. from Y to X orfrom Z to X) would use different B-VIDs. For resiliency, PE pairsmaintain primary and secondary PBT trunks which are monitored viaconnectivity check messages (CCMs).

The MPLS core provides PW instances interconnecting each pair of metros.A PW instance is created per PBT B-VID PW instances can provide the sametraffic profile as the PBT trunks, which allows the same QoS to beimplemented in the core network as in the metro networks.

For example, as shown in FIG. 9, assume that PE 2 is required totransmit frames to PE4 on PBT metro Y and is also required to transmitframes to PE 5 on PBT metro Z. If the MPLS core implements one PW perB-VID, S-PE1 may transmit frames to MSE1 intended for PE4 using (VID1,PE4) and may transmit frames to MSE1 intended for (VID2, PE5). The MSEis unaware where the PEs reside on the network but has a PW implementedper B-VID. Accordingly, the MSE may encapsulate the frames withB-VID=VID1 onto a PW to metro Y and may encapsulate the frames withB-VID=VID2 onto a PW to metro Z. Other MSEs would see different VIDs andassociate those VIDs with different PWs, which allows BVIDs to be reusedbetween different disjoint pairs of Metro networks. Additionally, theS-PEs do not need to add more information to the PBT frames at thehandoff to the MPLS network.

According to an embodiment, the MPLS core implements a PW for each PBTVID. The S-PE does not need to maintain any additional mappings andforwards regular PBT frames to the MPLS core. For each metro, each PBTB-VID is allocated such that it connects to a single other metro. Withinthe MPLS core PWs are implemented between each metro such that trafficmay be mapped according to the PBT B-VID to a PW in the MPLS core.

FIG. 10 shows an example encapsulation process that may be used toencapsulate traffic as it traverses a network having a single PBT domainimplemented across multiple PBT metro networks, with an MPLS core. Asshown in FIG. 10, when the U-PE transmits a frame to the PE it will beencapsulated with an Ethernet header 1002. The service frame includes aC-SA and A C-DA which are the MAC addresses associated with the serviceframe. Optionally, the service frame may include a C-Tag specified in802.1Q and an S-Tag specified in 802.1ad, although these tags are notrequired and will depend on the particular implementation of thecustomer network. The service tag will not change as the frame istransmitted across the network.

When the frame is received at the PE, the PE will perform PBBencapsulation specified in 802.1ah to add an I-SID, Ethertype, B-TAG,Ethertype, B-SA and B-DA. The B-SA is the MAC address of the PE thatreceived the frame from the customer, and the B-DA is the destinationMAC address of the PE on the PBT domain. According to an embodiment, theB-TAG may be selected to include a B-VID that specifies the destinationMetro network where the destination network element is located.Selecting the B-VID corresponding to the destination network allows theMPLS network to select a PW for the frame for use in transporting theframe across the MPLS network.

The PE will perform the PBB encapsulation and forward the frame across aPBT tunnel to the S-PE, which will forward the frame to the MSE on theedge of the MPLS network. The MSE will read the B-VID and use the B-VIDto select a PW for the frame. The MSE will then attach a PW label andLSP label and forward the frame across the MPLS network. The MSE mayalso apply a further link-layer Ethernet header to the frame which willbe stripped and replaced at each hop through the network.

FIG. 11 shows another embodiment in which PseudoWire (PW) signaling issupported end-to-end across the Ethernet network. In this embodiment,the service frame is considered the PW payload, and the U-PE or PE willattach a PW label 1102 to the PW payload for transmission across thenetwork. The PW label 1102 may also be referred to as a Virtual Channel(VC) label. The U-PE will also attach an Ethertype 1104 to allow theframe to be identified as PW encapsulated. The U-PE will also attach alink layer Ethernet header 1106 identifying the PE as the destination ofthe frame and the U-PE as the source of the frame. The Ethernet headermay also include one or more tags such as a C-Tag or an S-Tag (notshown).

When the PE receives the packet, it will strip off the customer header1106 and add a provider header 1108. The provider header 1108 includes aB-TAG (which includes a B-VID), an Ethertype, and the provider sourceand destination MAC Address (B-SA and B-DA). The B-VID will be selectedin this embodiment, as with the last embodiment, to identify the egressMetro network that contains the destination network element. The ingressPE on the PBT network will then forward the frame across a PBT trunk tothe S-PE.

The S-PE will forward the frame to the MSE, which will use the B-VID1110 to identify the PW, and attach a PW label 1112 and LSP label 1114to the packet. The MSE will then forward the packet across the LSP tothe destination metro network. Alternatively, where the MPLS network isimplementing VPLS, the MPLS network would implement a VPLS per B-VID,and make forwarding decisions based on B-DA. The egress MSE will stripthe PW and LSP labels off the packet and forward the packet to the S-PEof the egress metro. The Egress metro will forward the packet across thePBT trunk in the PBT network to the destination.

From an OAM standpoint, PBT trunk OAM maintenance entities may bemonitored on an end-to-end basis. When a PBT trunk fails, the head-endcan switch the services, represented by I-SIDs onto backup PBT trunks.When a PW fails, the MSE can notify via MS on the PBT trunk, if the MSEsupports Ethernet OAM. FIG. 12 shows some of the OAM maintenanceentities that may be implemented to support end to end OAM on the PBTtrunks within the network of FIGS. 9-11.

One of the advantages of interworking PBT metro networks with an MPLSnetwork are that the S-PEs are not required to introduce modificationsinto the data path to implement the handoff to the MPLS network.Additionally, the S-PEs do not need to maintain visibility to the I-SIDsor individual service instances. End-to-end trunk level OAM is possibleand is independent of the MPLS core. Additionally, end-to-end servicelevel OAM is also possible.

On the other hand, the end-to-end PBT OAM does not scale well. Themetros are also not autonomous, and need to have visibility into eachother's address space. OAM scaling issues, e.g. via AIS, can beaddressed but require Ethernet OAM support in the MSEs. Additionally,when the MPLS network is implementing VPLS, a MSE Virtual SwitchInstance (VSI) is required on a per-port basis, and the MSE will makeforwarding decisions based on the B-DA.

In the previous description it was assumed that the S-PE would forwardthe packets from the PBT network to the MPLS network without performingB-VID translation. It is possible to implement a mapping at the S-PEthat would allow B-VIDs to be translated so that the B-VID in use on thePBT network is not the same as the B-VID used on the MPLS network. Thishas implications with connectivity fault management, however, thereverse VLAN ID may be carried in the CFM payload. Thus, if the S-PE isperforming B-VID translation, the mapping would need to take placewithin the CFM payload or another mechanism would need to be implementedto cause the correct B-VID for the reverse path to be carried in the CFMpayload.

The PBT networks may be part of the same domain or, alternatively may beseparate domains. Where the PBT networks are separate domains, forexample if PBT metro X and PBT metro Y implement separate controlplanes, then the PBT trunk segments will not extend end-to-end acrossthe network. Rather, the S-PEs will maintain a mapping on a per-ISIDbasis to map traffic between trunk segments.

For example, as shown in FIGS. 13-14, the Ethernet access switch (U-PE)will hand off Ethernet frames (which may be encapsulated native serviceframes) to the PE. The PE offers an Ethernet UNI and either port-basedE-line service or tagged E-line service. The PE will thus use either theport, VLAN, or both to identify the service instance. The PE willencapsulate the frame in a PBT trunk within the metro, as shown in FIG.14, by assigning a service identifier (I-SID), B-Tag, and destinationMAC address (DA). The DA in this instance will be the DA of the S-PEthat will forward the traffic out of the metro network. The I-SID isrecommended to be end-to-end unique, but may be locally significant onlywithin each metro.

When the S-PE receives the frame it will determine the PBT segmentacross the MPLS core. As with the example discussed above, each metroallocates B-VIDs such that a particular B-VID is used only to connect toone other metro. The S-PE maintains a mapping of PBT segments and mapsthe traffic to the next PBT segment. The B-VID used for the segment isselected such that the B-VID will cause the frame to be forwarded acrossthe MPLS core to the correct metro.

When the MSE receives the frame, it will read the B-VID and place theframe onto a LSP/PW through the core to the correct metro by assigning aPW label and LSP label. The egress MSE will strip off the PW and LSPlabels and forward the frame to the S-PE on the metro. The S-PE willeither perform a second mapping to map the frame to a PBT trunk withinthe second metro or will directly forward the frame onto the trunkwithin the metro. This second option may exist where the PBT trunksegment extends from the second metro across the MPLS core. Where theframe is mapped to different trunk segments, the PBB header or portionsof the PBB header such as the B-DA and B-SA, B-VID, and I-SID may bechanged so that these values are unique within each PBT tunnel.

FIG. 15 shows multiple trunk segments extending end to end across anetwork having split PBT metro domains. The PBT trunk may be implementedto include several segments. For example, a first PBT trunk segment mayexist in PBT metro X, a second PBT trunk segment may extend betweenS-PEs on different metros across the MPLS network, and a third PBT trunksegment may extend across the PBT metro Y. Optionally, as mentionedabove, a two segment PBT path may be implemented such that either thefirst and second PBT trunk segments or the second and third trunksegments are implemented as a single trunk segment.

For resiliency, PE pairs maintain primary and secondary trunks, whichare monitored via connectivity check messages. The S-PE at the edge ofeach metro provides the interworking function. It is I-SID aware andmaintains, on a per-I-SID basis, a mapping between trunk segments thatextend over the PBT metro and the MPLS core. The mapping is maintainedin both directions so that the S-PE is able to map frames from a PBTtrunk on the metro to a PBT trunk on the core, and conversely from atrunk on the core to a trunk on the metro. The S-PE thus provides a UNIfunctionality to map frames to trunks on the PBT network. The MSEs willmap frames to PWs on a per-B-VID basis, so that the S-PE is not requiredto modify the format of the frames when passed to the MSEs.Alternatively, the S-PE may offer PW UNI to participate in PW signalingand apply PW labels to frames before they are forwarded onto the MPLScore.

Encapsulation of frames with different PBT domains interconnected withan MPLS core is the same as the encapsulation process described above inconnection with a unitary PBT domain extending across an MPLS core.However, since the S-PEs are mapping between PBT tunnels, thedestination address of the packet on each segment will be set to be theterminating device on that segment. Thus, for example in FIG. 15, PE2will create a header for use in the PBT network and use the MAC addressof S-PE1 as the destination address. S-PE1 will remove the MAC headerand create a new MAC header using the MAC address of S-PE3 as thedestination address. As noted above, the B-VID that is applied to theMAC header by S-PE1 will be the B-VID that allows the MSE to select a PWthat connects PBT metro X to PBT metro Y. Thus, although theencapsulation does not change, the end points of the PBT trunk segmentswill replace the values of the header with new values to reflectassociated with the new PBT trunk segment.

Each PBE trunk segment is monitored on an end-to-end basis by an OAMMaintenance Entity (ME). As shown in FIG. 16, each trunk segment whetherit extends across a metro, the core, or across both a metro and thecore, is monitored by an OAM ME. The particular resiliency strategy isdependent on the manner in which the PBT domain and the MPLS core areinterconnected. FIGS. 17-19 show three example ways in which the domainsmay be interconnected. In these Figs., FIG. 17 illustrates a full meshinterconnect, FIG. 18 illustrates a dual homed interconnect, and FIG. 19illustrates a square split multi-link trunking interconnect. Theinterconnect shown in FIG. 19 differs from that of FIG. 18 in that thetwo S-PEs in the interconnect of FIG. 19 share state and treat the linksextending between the network domains as a common link.

If a full mesh interconnect is in use (see FIG. 17), and a PBT trunkfails within a metro, the PE can detect it and switch over to anotherPBT trunk. None of the other domains are impacted by this type offailure. Similarly, if the PW in the MPLS domain fails, restoration doesnot impact the metro domains since the MPLS network may implement aroute around the failure in the MPLS network. If the S-PE fails, the PEneeds to switch the traffic to a different PBT trunk that shouldterminate at another S-PE. This requires the PE to switch to another PBTtrunk with potentially different VIDs and MAC DA.

If a dual homed interconnect is used, as shown in FIG. 18 or 19, and aPBT trunk fails in the metro, the PE will detect it and the S-PE candetermine which I-SIDs are affected by the failure. The S-PE can thensend Alarm Indication Signals (AIS) at the I-SID level on the PBT trunksacross the WAN core associated with those I-SIDs. If a PBT trunk acrossthe MPLS core fails, the S-PE can determine which I-SIDs are impactedand send Alarm Indication Signals at the I-SID level on PBT trunksacross the metro associated with those I-SIDs. Upon detecting a PBTtrunk failure or receiving an I-SID AIS notification, the PE can switchthe service instance (I-SID) to a backup PBT trunk. This type ofinterconnect thus requires the PE to switch to another PBT trunk withpotentially different VID and B-DA. The same behavior applies when anS-PE fails.

Some of the advantages associated with interworking split PBT metrodomains with an MPLS core are that the S-PE is not required to introduceany modifications to the data path. Thus, a normal S-PE should be ableto be used to implement an interworking of this nature. Additionally,OAM scaling issues are not severe, and end-to-end service levelmonitoring is possible. The metros are also able to remain autonomouswithout visibility into each other's address space, while a full mesh ofconnectivity between metros may be implemented across the MPLS core.

On the other hand, S-PEs are required to be I-SID (service instance)aware. The S-PEs need to change PBT trunks for I-SID flows and the S-PEsneed to be configured to map I-SIDs to PBT trunks in the Metro and overthe core. End-to-end trunk level OAM is not possible, and requiresnotification at the I-SID level.

If the customer is implementing OAM as well, and is not using S-taggedor C-tagged frames, or if the customer S-Tag or C-Tag is removed duringthe 802.1ah encapsulation process, then the ME level space may need tobe split so that both the customer and the provider may use the same MElevel space.

In the previous example, the S-PE was described as mapping PBT trunks ona per-I-SID basis. Optionally, where the I-SID is not end-to-end unique,the S-PE may also map I-SIDs so that different I-SID values may be usedfor the same flow in each of the trunk segments. In this instance, theS-PE would receive a frame, read the I-SID to determine the next PBTtrunk segment, and also use the I-SID to determine the I-SID to be usedas a service identifier on the next PBT trunk segment.

Similarly, the S-PE may map PW labels between domains, for example wherePW over PBT is being implemented (see FIG. 11) so that different PWlabel management may be used in each of the domains. The S-PE maytherefore implement PW label translation between PBT trunks as well asother types of mappings between PBT trunks. Where the p-bits are used toprovide a particular type of service on the PBT network, the S-PE or MSEmay map the p-bits to LSP EXP bits on the MPLS network. Additionally,the S-PE may map p-bits between PBT tunnels such that the same qualityof service (as determined by the p-bits) is implemented on both PBTtunnel segments.

It is also possible to implement PBB metros interconnected via an MPLScore. In this embodiment, the Ethernet access switch (U-PE) hands offEthernet frames to the metro access switch (PE). The PE uses the VLAN ID(VID) to identify the service instance (I-SID). The PE encapsulates theframe in a PBB tunnel and ships it across the PBB network. The I-SID isend-to-end unique. The B-VID and multicast address assignments that areused to create one or more PBB tunnels may be implemented via trafficengineering.

Resiliency is provided by redundant interconnects and by running xSTPacross a single domain joining the several metros. The MPLS coreprovides a VPLS service instance per B-VID that it is exposed to, andforwards traffic based on the B-DA. When offering VPLS, the MSE willprovide bridged Virtual Switch Instance (VSI) (not per port VSI) suchthat it can switch between different ports. When replication needs tooccur across the WAN, the MSE does so similar to VPLS. The S-PE is notrequired to maintain a special mapping in this case. Additional detailsassociated with PBB metros and an VPLS core are contained in U.S. patentapplication Ser. No. 11/540,023, entitled Method And Apparatus ForTransporting Ethernet Services, filed Sep. 30, 2006, the content ofwhich is hereby incorporated herein by reference.

In a network including PBB metros and an MPLS core, the PBB tunnels canbe monitored on an end-to-end basis. When an S-PE or MSE or NNI or linkwithin a metro fails, the spanning tree in use on the metro or the linkstate protocol (where the Ethernet metro is a link state protocolcontrolled Ethernet network) can address the failure via redundantpaths. If the failure leads to network segmentation, the PBB tunnelmonitoring will be able to detects this, however rectification of theproblem and restoration would require manual intervention.

Where failure occurs in the MPLS core, the MPLS network may have no wayto signal to the xSTP instance in the metro that the failure hasoccurred. Thus, the xSTP will not be able to initiaterestoration/reconvergence for an unacceptably long period of time or mayhave an unacceptable detection time. To mitigate this, a monitoringdomain may be implemented at the S-PEs to allow the S-PEs to implement aPBB segment Maintenance Entity (ME) across the segment of the PBB tunnelthat extends across the MPLS core network.

If a PBB segment ME indicates failure, the S-PE should trigger xSTPconvergence. Since the failure in the MPLS domain may not be propagatedinto the PBB network, when the connectivity fault management (CFM) beingrun across the PBB segment between the S-PEs (which spans the MPLSdomain) indicates a failure in the MPLS domain, the S-PEs shouldinitiate xSTP convergence assuming a failure on the PBB segment. Thisallows the network to reconverge quickly upon detection of a failure inthe MPLS network to allow a new set of PBB tunnels to be establishedthat can span the MPLS network and avoid the failed tunnel.

The S-PE is not required to be modified to enable PBB networks tointerconnect with MPLS core network and thus can implement an NNIhandoff to the MPLS core network. The S-PEs do not need to maintainvisibility to the I-SIDs or to individual service instances. A full meshof WAN connectivity may be implemented in the MPLS core network betweenall pairs of metros. Additionally, end-to-end service level monitoringis possible as is segment monitoring across the MPLS core.

However, since the PBB networks are implemented as a single large metrodomain, running a single xSTP spanning instance or link state protocolinstance, the large domain may make multicast domain difficult tomanage. Additionally, the metros are not autonomous and, thus, need tohave visibility into each other's address space. The metros are alsorequired to implement some form of loop avoidance technique, such asxSTP.

FIG. 20 illustrates an embodiment where the MPLS core implements PWs. Inthis embodiment, the Ethernet access switch (U-PE) will hand offEthernet frames to the metro access switch (PE). The PE uses the VLAN toidentify the service instance (I-SID), encapsulates the frame in a PBBtunnel, and transmits the frame across the PBB network. The I-SID isend-to-end unique. The B-VID and multicast address assignments areimplemented via engineering. At the S-PE, different physical interfacesare used to connect to different peer PBB domains. If the number ofinterfaces becomes a concern, aggregation structures may be employed.

By using a different physical interface on the S-PE for each destinationmetro, the MSE can implement a PW service instance on a per-port basis.Alternatively, the MSE may implement a PW service instance on aper-B-VID basis. The S-PE implements the equivalent of a Virtual SwitchInstance, since the S-PE is responsible for replicating frames tomultiple ports or outputting the frame using multiple B-VIDs. Thus, theMSE will receive the frame multiple times (once for each destinationMetro) and map the frames to PWs through the MPLS core to thedestination metros.

Where a link state protocol is in use on the PBB network, the S-PE mayview different interfaces as regular bridged ports and may use inherentbridge replication. Resiliency, in this instance, may be provided byimplementing redundant interconnects from the S-PE to the MPLS networkand running a common link state protocol instance across the several PBBnetworks.

From an encapsulation perspective, the service frame (which may or maynot contain the C-Tag and S-Tag) will be encapsulated using 802.1ah byPE2. Since the various PBB metros are implementing a common controlplane, PE will have visibility into PBB metro Y's address space and maycreate a provider MAC header that includes the MAC address of PE4 as thedestination MAC address (DA=PE4). Thus, the 802.1ah MAC header need notbe changed as the frame traverses the network.

When the frame is passed to the MSE at the ingress to the MPLS corenetwork, the MSE will map the frame based on the port on the S-PE overwhich it was sourced, or based on the B-VID, and apply a PW label and anLSP label to transport the frame across the MPLS network.

From a resiliency standpoint, the PBB tunnels can be monitored on anend-to-end basis. when an S-PE, MSE, NNI, or link within the metrofails, the link state protocol being run on the PBB metro may addressthe failure in a normal manner (i.e. via a redundant PBB tunnel). If thefailure leads to network segmentation, the failure will be detected bythe end-to-end Maintenance Entity, but correction will require manualintervention.

If a failure occurs in the MPLS core, the MPLS network may not be ableto signal the failure to the PBB metro networks. This may result in thePBB networks being unable to initiate reconvergence/restoration withinan acceptable period of time. Accordingly, the S-PEs may implement a PBBsegment ME across the MPLS core to allow the S-PEs to detect a failurewithin the MPLS network. Upon detection of a fault on the PBB segment MEextending between the S-PEs across the MPLS core, the S-PEs may initiatexSTP reconvergence or link state protocol reconvergence to allow the PBBnetwork to route traffic around the failure. Thus, if the PBB segment MEindicates failure, the link state protocol should be notified to triggerconvergence. This allows reconvergence to be initiated without explicitnotification of the failure from the MPLS network to the PBB networks.

The S-PE does not require modification to the data path to implementhandoffs to the MPLS network. The S-PEs also are not required tomaintain visibility to the I-SID or individual service instances. A fullmesh of connectivity between metros may be implemented in the MPLS core,and end-to-end service level monitoring is possible.

On the other-hand, implementing one big metro domain across the severalmetro networks means that the multicast domain is concomitantly largeand, hence, difficult to manage. Metros are also not autonomous, andneed to have visibility into each other's address space. A loopavoidance technique, such as reverse path forwarding check implementedin connection with a link state protocol such as Open Shortest PathFirst (OSPF) or Intermediate System to Intermediate System (IS-IS) isalso required.

In addition to implementing the PBB metros as one domain, it is possibleto run different xSTP or link state protocol control instances in eachof the PBB metros to allow the metros to be independent. Where split PBBmetros are interconnected across an MPLS domain, the PBB metros willimplement PBB tunnels between the PEs and S-PEs. The I-SID in this casemay be end-to-end unique or may be metro-specific. Resiliency isprovided by redundant interconnects between the PBB metros and the PLSBcore, and by running xSTP within each domain—i.e. each PBB metro runsits own xSTP instance.

The MPLS core provides VPLS service instance per B-VID that it isexposed to. B-VLAN IDs are allocated based on per-connectivity requiredacross metros. Thus, if there are five metros, 24 VPLS instances will berequired to interconnect the metros (10 connecting each metro pair, 9connecting 3 each, 4 connecting 4 each, and 1 connecting all of themetros).

When a frame is received at the PE in metro X it will be encapsulatedusing 802.1ah and mapped to a PBB tunnel within metro X. If the C-DA ofthe frame that is received by the PE is unknown to the PE, the PE willmap the frame to a multicast MAC DA in the B-VID tunnel (PBB tunnel).The S-PE terminates the B-VID tunnel, and maps the B-VID tunnel acrossthe WAN, which means that the S-PE maintains a mapping between I-SID orC-DA and corresponding B-VID tunnel and B-DA for use in across the MPLScore in a manner similar to the mapping maintained by the PE.Additionally, the receiving S-PE will map the received frame to a B-VIDtunnel across Metro Y.

Within the MPLS core, the MSE treats the frames like regular Ethernetframes. Since the MPLS core has implemented VPLS service instances on aper-B-VID basis, the MSE will map the frame using the B-VID to a VPLSservice instance and forward it across the MPLS network. The Ethernetframes will be received by one or more egress metros to be forwardedonto those metro networks.

Thus, in this embodiment, the S-PE maintains a mapping of I-SID and C-DAto B-VID and B-MAC in both directions. The S-PEs also run xSTP or a linkstate protocol in the control plane and in the MPLS WAN using distinctV-LAN space. The S-PE will also correlate failures between the Metro andMPLS core domains to block/unblock forwarding states depending on thestate of the networks.

From a resiliency standpoint, the PBB domain will be able to detect andcorrect for failures that occur within the PBB domain. The MPLS domainmay have no way of signaling failures that occur in the MPLS core,however. Thus, the S-PEs may implement OAM maintenance entities acrossthe core to detect for failure in the MPLS core and initiatereconvergence in the PBB network upon detection of a failure on the PBBsegment maintenance entity.

Since the PBB domains are separate domains, the S-PE is required to mapflows between PBB tunnels. Accordingly, the S-PE will map flows from onePBB tunnel to the other PBB tunnel based on the I-SID or the C-DA. Thus,the S-PE maintains a mapping to enable it to perform the mapping betweenI-SID and target PBB Tunnels. The S-PE may also translate other values,such as B-VID, to allow for independent B-VID management in differentdomains. Similarly, the S-PE may maintain a table of ingress multicastDA and egress multicast DA to allow for translation of multicast DAbetween domains. This may be particular useful where the metro domainallocates multicast DAs using an algorithm different than that used bythe core PLSB domain, i.e. when the core uses an I-SID unique multicastDA. The S-PE is also required to support control xSTP instances, whichallows the S-PE to block data forwarding for particular sets of VIDs.

Split PBB domains may be implemented and interconnected by an MPLSnetwork providing PW service, where the S-PEs are not configured toperform B-VID translation. In this instance, the S-PEs would run acontrol instance such as xSTP or a link state protocol, to enable theS-PEs to implement a common control plane. This allows the S-PEs toblock data forwarding for particular sets of B-VIDs.

In this embodiment, the S-PE will switch flows from PBB NNI to PBB NNIbased on I-SID. The S-PE will thus maintain a mapping of I-SIDs to PBBtunnels and maintain a table of ingress multicast DA and egressmulticast DA to allow translation of multicast DA between tunnels. Thisis needed where the metro domain allocates multicast DA using analgorithm that is different than the algorithm used by the core domain,which uses I-SID unique multicast DAs. Optionally, the S-PE may allowB-VID translation between tunnels so that independent management ofB-VID may occur in the different domains. For resiliency, the S-PEshould implement segment PBB tunnel maintenance entities to detectfaults on the MPLS network, and trigger xSTP or link state protocolreconvergence upon detection of a failure. Additionally, the S-PE mayallow for I-SID translation between PBB tunnels to allow for independentmanagement of I-SIDs in different domains.

Implementing split PBB domains reduces the size of the xSTP or linkstate protocol domains, which makes the domains more manageable from acontrol standpoint. Additionally, the metros are autonomous, so thatthey do not need to have visibility into each other's address spaceexcept at the S-PE. A full mesh of connectivity may be supported in thecore network between each pairs of metros. Additionally, end-to-endservice level monitoring is possible.

However, the S-PEs are required to be I-SID aware and C-MAC aware. TheS-PE needs to provide a mapping between PBB tunnels and B-MACs based onthe I-SID and C-MAC. It also requires coordination of failures withindifferent instances of xSTP or link state routing protocol at the S-PE.The solution also requires the use of some loop avoidance technique,such as implementation of xSTP or link state routing protocol in thecontrol plane.

FIGS. 22 and 23 show another interconnection scenario in which bothPBB/PBT and MPLS metros are interconnected across an MPLS core networkimplementing VPLS service. Services, in this scenario, will be assumedto be driven from an MPLS standpoint—what an MPLS network might beoffering. For example, an MPLS metro may offer VPLS service or PWservice. For end-to-end PW service, the PBT/PBB metro will offer PW overPBT, and the MPLS metro may implement PWs. For end-to-end VPLS, thePBT/PBB metro will implement PBB tunnels while the MPLS metro mayimplement VPLS or PW spokes.

In the embodiment shown in FIG. 22, the access switch (U-PE) hands offnative service frames to the PBB/PBT access switch (PE) to be carriedtransparently over a PW service. The PE may encapsulate different nativeservices using PW over PBT. In the other direction, the access switchwill hand off native service frames to the MPLS access switch (N-PE)which will encapsulate the native services to be carried transparentlyover a PW service. The PE and N-PE establish an end-to-end PW. The PEand N-PE is not necessarily aware of the other metro, however.

An end-to-end PW may be established manually via a network managementplane or via signaling in the control plane. If MS-PW signaling is used,then the PE and N-PE would serve as terminating PEs (T-PEs) and the S-PEand MS-PE would serve as switching PEs (S-PEs). Optionally the MSE canalso act as an S-PE.

FIG. 23 shows the encapsulation of traffic as it passes across thenetwork of FIG. 22. As shown in FIG. 23, when PE2 receives a packet itencapsulates the packet with a PW label. PE2 may provide encapsulationfor different types of traffic, i.e. different native type UNIs. The PEwill also apply a MAC header to the packet to place the packet onto aPBT trunk through the metro network X.

When the S-PE receives the packet, it will remove the MAC header and usethe PW label to map the packet to a PBT trunk across the MPLS core. TheS-PE thus maintains a mapping between PBT trunks in either directionbased on PW label.

The MPLS core will provide VPLS instances for each B-VID that it isexposed to, which would thus not require the metro to make anymodifications to frames across the NNI. Thus, the B-VID of the PBT trunkacross the MPLS core may be selected according to the VPLS instance thatis to be used to transport the packet to one or more destination metros.

When the MPLS metro receives the packet, the MS-PE on the MPLS metro(MS-PE3 in FIG. 23) would treat the frames as link local tagged frames.Thus, the MS-PE will remove the Ethernet encapsulation header and treatthe frames as PW frames. The MS-PE will thus read the PW label and applya LSP label to forward the packet across the MPLS network. The MS-PE isrequired, in this instance, to support static PW UNI to enable it toread the PW and select a LSP for the packet.

From a resiliency standpoint, each PBT trunk may be monitored on anend-to-end basis by implementing a PBT trunk maintenance entity. In theMPLS domain the path may be monitored via an MPLS LSP maintenanceentity. The end-to-end service may also be monitored using a PW VirtualCircuit Connection Verification (VCCV) or via MS-PW OAM.

Advantageously, no modifications are required to the data path athandoff. Additionally, the PWs that are required to be set up in theMPLS core scale on the order of O(n), where n is the number of Metrosconnected to the MPLS core. Also, a full mesh of connectivity may beimplemented between the metros. The metros are autonomous, and thus donot need to have visibility into each other's address space.Additionally, end-to-end service level monitoring is possible.

On the other hand, S-PEs are PW label (service instance) aware. Inaddition to PBT trunk configurations, S-PEs need to be configured to mapPW labels to the PBT trunks in both directions (into the PBT metro andinto the MPLS core). End-to-end trunk level OAM is not possible, andrequires notification at the PW level. The MS-PE will also be requiredto support a static PW UNI, if MS-PW signaling is not used.

In summary, the S-PEs switch flows from PBT-NNI to PBT-NNI (between PBTTrunks) based on the PW label (where PW over PBT is used in the PBTnetwork). The PE and S-PE also support VCCV OAM on the PW to monitor theservice on an end-to-end basis. When the S-PE detects a failure of a PBTtrunk, it will determine the PWs affected by the failure and generate anAlarm Indication Signal (AIS) at the PW level on the corresponding PBTtrunk. Optionally, trunks may be implemented as PBT trunk groups formonitoring purposes.

The S-PE may implement several additional features to reduce the amountof interdependence between the domains. For example, the S-PE may allowPW label translation between PBT trunks, to allow for independentmanagement of I-SIDs in the different domains. Additionally, the S-PEmay implement B-VID translation between PBT trunks and may alsoimplement DA translation between PBT trunks. This solution requires theMS-PE to support a static PW UNI.

FIGS. 24-25 show a scenario in which the MPLS core that interconnectsthe PBT and MPLS metros is implements PWs rather than VPLS serviceinstances.

In the scenario shown in FIGS. 24-25, the access switch (U-PE) will handoff native service frames to the MPLS/PBT access switch (N-PE/PE) to becarried transparently over a PW service. The N-PE may encapsulatedifferent native services (e.g. TDM) over the PW. The PE may encapsulatedifferent native services over PWoPBT. The N-PE and PEs establishend-to-end PWs to be used to carry the traffic across the network. ThePE and N-PE, however, are not necessarily aware of the other metro.

End-to-end PWs may be established by manual provisioning at themanagement plane or by PW signaling in the control plane. If MS-PWsignaling is used, then the PE and N-PE would serve as terminating PEsand the S-PE and MS-PE would serve as switching PEs (S-PEs). The MSE mayalso act as a switching PE if desired.

FIG. 25 shows the encapsulations that may be used to transport theservice frame (payload) across the network. As shown in FIG. 25, when aPE receives a packet from the U-PE, it will encapsulate it with a PWlabel and also apply a MAC header to place the Packet onto a PBT tunnelacross the PBT metro. When the S-PE receives the packet, it terminatesthe PBT tunnel and removes the MAC header. The S-PE provides a mappingof PW label to PBT trunks in the metro direction, and maintains amapping of PBT trunk to PW label in the direction of the MPLS core.

The S-PE will remove the PBT trunk MAC header and apply a link level MACheader and forward the packet to the MSE. The MSE will strip off thelink MAC header, read the PW label, and apply a LSP label to forward thepacket across the MPLS network. The egress MSE will remove the LSPlabel, read the PW label, and apply a link level MAC header to forwardthe packet to the MPLS metro Y. The MS-PE will remove the link level MACheader, read the PW label, and apply a LSP label to forward the packetacross the MPLS metro network Y. The egress N-PE will remove the PWlabel and forward the packet to the U-PE.

From a resiliency standpoint, each PBT trunk ME may be monitored on anend-to-end basis in each domain. In the MPLS domain, the trunk may bemonitored by monitoring the MPLS LSP. The end-to-end service may also bemonitored by using a PW Virtual Circuit Connectivity Verification andMS-PW OAM.

The scenario has similar advantages/disadvantages as the scenariodescribed above with respect to FIGS. 22 and 23 in which the MPLS coreoffered VPLS service rather than PW service. However, in this instanceMS-PW signaling is required to be implemented across the PE, S-PE, MSE,and MS-PE.

FIG. 25A shows another encapsulation scenario in which the U-PEimplements PW encapsulation prior to forwarding the packet to the PE.Thus, in this example the PW label is applied at the U-PE before beingtransmitted to the PE, rather than having the ingress PE apply the PWlabel to the frame. The other encapsulation processes described abovewith respect to FIG. 25 may be used to transport this frame across thenetwork.

In the previous two scenarios, it was assumed that the PW was maintainedend-to-end. Optionally, the PW may be switched (mapped) at one or morelocations along the end-to-end path to enable the domains to remainindependent. For example, the S-PE may map PW labels in addition tomapping packets to/from PBT tunnels on a PW basis. This allows differentPWs to be used in the PBB/PBT metro X than are used in the MPLS core.Similarly, the MSE may map PWs to allow different PW labels to be usedin the interconnect than are used in the MPLS core. Likewise, the MS-PEmay map PW labels to allow different PW labels to be used in the MPLSmetro Y than are used in the MPLS core. Thus, many different mappingsmay occur depending on which nodes on the network are configured to mapparameters for the packet as the packet is passed along a path on thenetwork.

The network elements described above, such as the PE and S-PE, as wellas the MSE and N-PE, are all conventional network elements. The networkelements are programmed, however, or have hardware implementations, thatwill enable them to perform the functions described above to placetraffic on tunnels through the network and to switch traffic from tunnelsegments. Similarly, the network elements include software, hardware,and/or firmware that will enable the network elements to participate inOAM maintenance entities and other OAM flows to enable appropriatemonitoring to occur as described in greater detail above. Thus, theinvention is not limited to any particular hardware implementation asmany different network element hardware platforms have been created overthe years and are likely to be created in the future as network elementscontinue to evolve.

Thus, it will be apparent to a skilled artisan that all logic describedherein can be embodied using discrete components, integrated circuitrysuch as an Application Specific Integrated Circuit (ASIC), programmablelogic used in conjunction with a programmable logic device such as aField Programmable Gate Array (FPGA) or microprocessor, or any otherdevice including any combination thereof. Programmable logic can befixed temporarily or permanently in a tangible medium such as aread-only memory chip, a computer memory, a disk, or other storagemedium. Programmable logic can also be fixed in a computer data signalembodied in a carrier wave, allowing the programmable logic to betransmitted over an interface such as a computer bus or communicationnetwork. All such embodiments are intended to fall within the scope ofthe present invention.

It should be understood that various changes and modifications of theembodiments shown in the drawings and described in the specification maybe made within the spirit and scope of the present invention.Accordingly, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings be interpreted in anillustrative and not in a limiting sense. The invention is limited onlyas defined in the following claims and the equivalents thereto.

What is claimed is:
 1. A method of transporting customer Ethernet framesover a Multi-Protocol Label Switching (MPLS) network implementing apseudo-wire service, the method comprising: receiving a customer frameon a network port, the customer frame including a customer destinationMAC address (C-DA) and a customer source MAC address (C-SA); identifyinga customer service instance based on at least one of the network portand a VLAN associated with the frame; encapsulating the customer framewith a backbone destination MAC address (B-DA), a backbone source MACaddress (B-SA), and information identifying the customer serviceinstance associated with the frame, the B-DA being selected based on thecustomer service instance; further encapsulating the customer frame witha Label Switched Path (LSP) label and a pseudo-wire label, thepseudo-wire label being selected based on the information identifyingthe customer service instance and the LSP label being selected based onthe B-DA; and forwarding the encapsulated frame toward a network nodeassociated with the B-DA based on the LSP label.
 2. The method of claim1, wherein encapsulating the customer frame with the B-DA, the B-SA andthe information identifying the customer service instance comprisesMAC-in-MAC encapsulation.
 3. The method of claim 1, wherein theinformation identifying the customer service instance comprises anI-SID.
 4. The method of claim 1, wherein the information identifying thecustomer service instance comprises a Virtual Local Area Networkidentifier (VLAN-ID).
 5. The method of claim 1, wherein the VLAN-ID ispart of a B-Tag.
 6. The method of claim 1, wherein: receiving thecustomer frame on the network port comprises receiving the customerframe at an edge node of a first access network; encapsulating thecustomer frame with the B-DA, B-SA and information identifying thecustomer service instance comprises encapsulating the customer frame atthe edge node for forwarding over the first access network; and furtherencapsulating the customer frame with an LSP label and a pseudo-wirelabel comprises further encapsulating the customer frame at an edge nodeof a core network for forwarding over the core network to a secondaccess network.
 7. The method of claim 6, wherein the informationidentifying the customer service instance comprises an I-SID.
 8. Themethod of claim 6, wherein the edge node of the first access networkidentifies the I-SID based on a Virtual Local Area Network identifier(VLAN-ID) of the customer frame.
 9. The method of claim 8, wherein theVLAN-ID is part of a B-Tag.
 10. The method of claim 6, furthercomprising forwarding the customer frame over the second access networktoward its destination.
 11. The method of claim 10, further comprising:decapsulating the further encapsulated customer frame by removing theLSP label, the pseudo-wire label, the B-DA, the B-SA, the informationidentifying the customer service instance; and forwarding the customerframe toward its destination over the second access network based atleast on the C-DA.
 12. The method of claim 11, wherein: the framecomprises a customer Virtual Local Area Network identifier (C-VLAN); andforwarding the customer frame toward its destination over the secondaccess network based at least on the C-DA comprises forwarding thecustomer frame based on its C-DA and its C-VLAN.
 13. The method of claim6, wherein the first access network comprises a Provider BackboneTransport (PBT) network.
 14. The method of claim 6, wherein the firstaccess network is a Provider Backbone Bridging (PBB) network.
 15. Themethod of claim 6, wherein the first access network is a Provider LinkState Bridging (PLSB) network.
 16. The method of claim 6, wherein thesecond access network comprises a Provider Backbone Transport (PBT)network.
 17. The method of claim 6, wherein the second access network isa Provider Backbone Bridging (PBB) network.
 18. The method of claim 6,wherein the second access network is a Provider Link State Bridging(PLSB) network.
 19. The method of claim 6, wherein the second accessnetwork is an MPLS network.